1. Field of the Invention
The present invention refers to a new and useful process for the preparation of para sulfonated calixarenes. In particular, the invention relates to a process for the preparation of calixarene p-sulfonic acids starting from calixarenes which are para substituted by a blocking group, e.g. p-alkyl calixarenes.
Calixarenes are macrocyclic phenolic compounds that are generally prepared from phenolic compounds by condensation in an acid or basic environment with an aldehyde such as formaldehyde, an alkylaldehyde, an arylaldehyde, or a heteroarylaldehyde, preferably formaldehyde. These macrocycles which are shortly named "calixarenes" are of the type of tetra-p-tert-butyl-calix4!arenes or pentacyclo-19.3.1..sup.13,7.1.sup.9,13.1.sup.15,19 !octacosa-1(25),3,5,7(28),9,11,13(27),15,17,19(26),21,23-dodecaene and their analogous compounds, namely the 5!, 6!, 7!, 8!, 9! and 10! arene analogues.
The utility of the calixarenes is based on their capability of forming complexes, adducts and/or inclusion compounds with neutral or ionic organic and inorganic compounds; furthermore, calixarenes are outstandingly stable and resistant to high temperatures and chemical attacks in aggressive environments.
A serious problem which is encountered in the industrial application of these macrocycles stems from their insolubility in protic solvents such as water and the alcohols. One possibility of overcoming this problem and to make them soluble is to introduce solubilizing groups, preferably sulfonic acid groups, in the para position to the hydroxy groups in the phenolic nuclei, giving sulfonated calixarenes. Such water soluble calixarene derivatives have proven to be useful in a great number of fields, especially in pharmacology, and still more application fields are currently opened, such as catalysts or catalyst intermediates.
2. Description of the Prior Art
Sulfonation of calixarenes that are unsubstituted in the para position of the phenolic OH group has already become known, see, e.g., Japanese patent No. 61-083156 to Sugai Chemical Industry Co. Ltd. However, calixarenes must be prepared from para substituted phenols where this para substituent is a blocking group to render the para position inaccessible; otherwise, a free para position of the phenol does not yield appreciable amounts of calixarenes during reaction with aldehydes but rather the well known phenolic resins. Therefore, it is necessary in the synthesis of calixarenes to start from para substituted phenols. Of course, such starting phenols are preferred where the para blocking substituent is rather easily removable; such substituents are, e.g., alkyl groups such as the tert-butyl group.
Until now, sulfonation of para alkyl substituted calixarenes has been effected by a multistep process. First, the para alkylated calixarene is prepared which is then dealkylated by an reversed Friedel-Crafts reaction to yield the para unsubstituted calixarenes. In a further step, the calixarene is reacted with hot concentrated sulfuric acid.